How to Define Format When Using Pandas To_Datetime?
I Want to Plot Result vs Time Based on a Testresult. Csv File That Has Following Format, and I Have Trouble to Get the Time Column's Datatype Defined Properly...
I want to plot RESULT vs TIME based on a testresult.csv file that has following format, and I have trouble to get the TIME column's datatype defined properly.
TIME,RESULT
03/24/2016 12:27:11 AM,2
03/24/2016 12:28:41 AM,76
03/24/2016 12:37:23 AM,19
03/24/2016 12:38:44 AM,68
03/24/2016 12:42:02 AM,44
...
To read the csv file, this is the code I wrote:
raw_df = pd.read_csv('testresult.csv', index_col=None, parse_dates=['TIME'], infer_datetime_format=True)
This code works, but it is extremely slow, and I assume that the infer_datetime_format takes time. So I tried to read in the csv by default first, and then convert the object dtype 'TIME' to datetime dtype by using to_datetime(), and I hope by defining the format, it might expedite the speed.
raw_df = pd.read_csv('testresult.csv')
raw_df.loc['NEWTIME'] = pd.to_datetime(raw_df['TIME'], format='%m/%d%Y %-I%M%S %p')
This code complained error:
"ValueError: '-' is a bad directive in format '%m/%d%Y %-I%M%S %p'"
2 Answers
The format you are passing is invalid. The dash between the % and the I is not supposed to be there.
df['TIME'] = pd.to_datetime(df['TIME'], format="%m/%d/%Y %I:%M:%S %p")
This will convert your TIME column to a datetime.
Alternatively, you can adjust your read_csv call to do this:
pd.read_csv('testresult.csv', parse_dates=['TIME'],
date_parser=lambda x: pd.to_datetime(x, format='%m/%d/%Y %I:%M:%S %p'))
Again, this uses the appropriate format with out the extra -, but it also passes in the format to the date_parser parameter instead of having pandas attempt to guess it with the infer_datetime_format parameter.
you can try this:
In [69]: df = pd.read_csv(fn, parse_dates=[0],
date_parser=lambda x: pd.to_datetime(x, format='%m/%d/%Y %I:%M:%S %p'))
In [70]: df
Out[70]:
TIME RESULT
0 2016-03-24 00:27:11 2
1 2016-03-24 00:28:41 76
2 2016-03-24 00:37:23 19
3 2016-03-24 00:38:44 68
4 2016-03-24 00:42:02 44
Maya is a hardware enthusiast who tests and reviews smart home devices, smartphones, wearables, and audio gear. She focuses on practical consumer value and build quality.
